Chapter 7
Detection of Adulterated Fruit Flavors Dana A. Krueger
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Krueger Food Laboratories, Inc., 24 Blackstone Street, Cambridge, MA 02139
Methods employed in the detection of synthetic and artificial flavors are surveyed. GC and HPCL techniques are used to detect substances not naturally presnent in flavors from particular source materials. Capillary GC-MS is used to identify the presence of substances which are not nature-identical. Chiral GC, HPLC and enzymatic techniques are used to identify synthetic racemates substituted for chiral flavoring materials. Carbon 14 analysis is used for identification of petrochemical synthetics. Applications of isotope ratio mass spectrometry and deuterium N M R analysis for differentiating natural and synthetic flavor compounds are discussed. The marketplace for fruit products, flavors, and syrups has for many years been plagued by the problem of economic adulteration. Economic adulteration is the undeclared substitution for a high valued product of a similar, but inferior and less expensive product. Many natural flavoring materials are much more expensive to produce than corresponding artificial materials, and command much higher prices. This provides a large incentive for this type of adulteration; one which has led to a long history of problems in the flavor trade. Natural flavors are produced from animal or plant sources by one or more of several "physical" processes. These physical processes include mechanical expression, distillation or solvent extraction. Also included among these processes are the chemical processes of pyrolysis, fermentation and enzymatic reaction. Flavoring materials produced in this manner may properly be called natural. The regulatory regime in the United States recognizes several types of flavor label descriptions. Natural flavors may be claimed to be natural and from particular defined sources, such as bitter almond oil or apple essence. Alternatively, they may simply be labeled natural flavor, with no reference to the particular flavoring ingredients. A l lflavoringmaterials which are not prepared from the approved natural
0097-6156/95/0596-0070$12.00/0 © 1995 American Chemical Society In Fruit Flavors; Rouseff, R., et al.; ACS Symposium Series; American Chemical Society: Washington, DC, 1995.
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7.
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sources and processes are properly labeled as artificial. In the European Community, the American artificial category is further subdivided. Synthetic substances are labeled "nature identical" if the same chemical substance occurs in natural foodstuffs, while substances unknown in nature are labeled artificial. This hierarchy of flavor labeling allows the possibility of three different types of mislabeled or adulterated flavors. A defined source type of flavor would be considered adulterated if it contained additions of any other type of flavor. A natural flavor would be considered adulterated if it contained additions of any synthetic flavoring material. Finally, in European Community countries, a nature identical flavor would be considered adulterated if it contained additions of a synthetic substance of a type which does not occur in nature. As the producers of fraudulent products become ever more clever in their formulations, substituting artificial for natural flavorings, the quality control analyst requires ever more sophisticated tools for the detection of these products. This article surveys some techniques for the analysis of natural fruit flavorings that have proved useful in detecting economic adulteration. The techniques are illustrated by examples taken from the author's work and from the literature.
Detection of Foreign Components in Defined Source Flavors Many fruit flavored products are labeled as being flavored solely by the juice or essence of the fruit in question. Such a product would be mislabeled if the flavoring was in fact derived in whole or part from another material. Such adulterations can often be detected by analysis for substances in the product which are not normally found in the fruit. One of the key flavor impact substances of black currant juice is the sulfur containing substance 4-methoxy-2-methyl-2-mercaptobutane. This substance is responsible for the catty odor of black currants. The essential oil of the buchu plant contains a different substance with a similar aroma. Many imitation black currant flavors utilize buchu oil for the catty note. Buchu oil contains as major constituents isomers of diosphenol, which are not found in black currants. Adulteration of natural black currant products has been detected by capillary gc-ms analysis of the volatile substances. The presence of buchu oil diosphenols is readily detected by this procedure (/). Passion fruit juice is a strongly flavored juice which is very popular in the formulation of nectars and blended fruit juice drinks. Adulteration of passion fruit juice by dilution with orange juice is an occasional problem. Such adulteration can be detected by analysis for substances typical of orange juice. Capillary gc-ms analysis of the volatile substances of passion fruit juice will reveal the presence of significant levels of limonene and other orange oil terpenenes in such adulterated juices. Pure passion fruit contains only traces of limonene (2). Examination of the phenolic substances of passion fruit by hplc analysis will also reveal the presence of hesperidin, a substance found in orange juice, but not in passion fruit juice, in such cases. (3).
In Fruit Flavors; Rouseff, R., et al.; ACS Symposium Series; American Chemical Society: Washington, DC, 1995.
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FRUIT FLAVORS
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Detection of Components Not Found in Nature Many artificial flavors are formulated from substances which are not found in natural foodstuffs. Many adulterated flavors can be detected by analysis for such substances. An important flavor impact compound of strawberry juice is 2,5-dimethyl4-hydroxy-2,3-dihydrofuran-3-one or furaneol. Many formulated strawberry flavors achieve a similar impact through the use of the substituted pyrans maltol and ethyl maltol. Ethyl maltol, which has a particularly intense aroma, is a substance not found in nature. The author, by capillary gc-ms analysis, has found numerous instances of supposedly natural strawberry flavors which contain ethyl maltol, and are thus in fact artificial. Vanillin is also an important flavor constituent in many natural fruit flavors. The author has found occasional instances by gc-ms analysis where the more intense substance ethyl vanillin has been used in flavors labeled as natural. Ethyl vanillin is also a substance not found in nature.
Detection of Manufacturing Impurities in Synthetic Flavoring Materials Many artificial flavor chemicals contain traces of impurities which are minor byproducts of their synthesis. These trace substances can be used as markers to indicate the synthetic origin of the substance. Linalool 1 is a substance which is used in the formulation of many fruit flavors, particularly apricot and peach flavors. Natural linalool is obtained from a number of essential oils. Synthetic linalool is manufactured by the hydrogénation of an intermediate, dehydrolinalool 2. After partial hydrogénation of 2 to linalool, a small quantity of the fully hydrogenated product, tetrahydolinalool 3 is formed. Synthetic linalool usually contains residual trace quantities of 2 and 3. Capillary gc-ms analysis of linalool can be used for the detection of 2 and 3, and can thus be used for the detection of synthetic linalool (4).
Cinnamaldehyde 4 is a substance which is used to add a spicy note to many formulated flavors. Natural cinnamaldehyde is obtained from cassia and cinnamon oils. Synthetic cinnamaldehyde is prepared by the condensation of acetaldeyde with benzaldehyde. During synthesis, a small quantity of a product resulting from the condensation of two molecules of acetaldehyde, 5-phenylpentadienal 5, is formed.
In Fruit Flavors; Rouseff, R., et al.; ACS Symposium Series; American Chemical Society: Washington, DC, 1995.
7. KRUEGER
Detection of Adulterated Fruit Flavors
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Capillary gc-ms analysis of cinnamaldehyde can be used to detect traces of 5, and can thus be used for the detection of synthetic cinnamaldehyde (5).
Determination of Carbon 14 Content Analysis of the natural radiocarbon content of foodstuffs has been used as a tool to distinguish between natural products and synthetics from fossil fuel sources. Atmospheric C 0 , and natural products derived from it via plant photosynthesis, contains minute quantities of the radioactive isotope C . Since C has a radioactive half-life of approximately 6000 years, carbon from fossil fuel sources which has been in place for millions of years is essentially devoid of C, it having long since decayed away. Therefore C analysis can be used as a sensitive indicator of carbon from fossil fuel sources, and consequently of many synthetic flavor chemicals. The use of C analysis for the detection of synthetic flavoring materials was first suggested for vinegar in 1952 (6). C content is determined by radiation counting of a suitable derivative using a liquid scintillation counter or a gas proportional counter. It has since been applied to caffeine (7), cinnamaldehyde (8), and other flavor chemicals. Benzaldehyde is the major flavor impact compound of cherry juice; natural benzaldehyde is used in the formulation of natural cherry flavors. The author showed that C analysis can be used to differentiate natural from synthetic benzaldehyde (9). 2
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Benzaldehyde Source ex Apricot Kernels Synthetic
'C Activity (dpm/gC) 15.7
